Electrocatalytic reduction of nitric oxide on Pt nanocrystals of different shape in sulfuric acid solutions

Pt tetrahexahedral (Pt-THH) nanocrystals enclosed with 24 {h k 0} facets, Pt nanothorns (Pt-Thorn) with a high surface density of atomic steps, and congeries of Pt nanoparticles (Pt-NP) were prepared and served as catalysts to study the electrocatalytic reduction of both adsorbed and solution nitric oxide. The structure sensitivity for the reduction of a saturated NO adlayer on the Pt nanocrystals (NCs) of different shape was studied by cyclic voltammetry (CV) and in situ FTIR spectroscopy in sulphuric acid solutions. The results revealed that two types of NO adsorbates can be reduced independently at separated potentials, i.e. the reduction of linear bonded NO (NOL) on the Pt-NP electrode gives rise to a current peak at −0.01 V (vs. SCE), while the bridge adsorbed NO (NOB) yields a current peak at −0.08 V. The in situ SNIFTIRS results confirmed the assignment of NO adsorbates, i.e. the NOB species yielding a IR absorption bipolar band with its negative-going peak at 1636 cm−1 and positive-going peak around 1610 cm−1, and the NOL species giving rise to a bipolar band with its negative-going peak at 1809 cm−1 and positive-going peak around 1720 cm−1. It has determined that the NOL species can be preferentially formed on the Pt NCs with open surface structure, i.e. the more open the surface structure of the Pt NCs, the larger the relative quantity of NOL versus NOB. It has also revealed that the Pt NCs with a high surface density of atomic steps exhibit superior electrocatalytic activity for the reduction of solution NO species. The steady-state current density of NO reduction on Pt-THH NCs is 7.5–12 times as large as that on Pt-NP, and that on Pt-Thorn is 2.5–4 times of that on Pt-NP in the reduction potential region of electrochemical dynamic control.